The Palaeoproterozoic Kangerluluk gold-copper mineralization (southeast Greenland): Pb and Nd isotopic constraints on its timing and genesis

The Ketilidian Mobile Belt (KMB) in South Greenland is dominated by the Pal aeoproterozoic Julianehab Batholith (1,850-1,770 Ma) and is bordered by sup racrustal sequences. The batholith is composed of granite, granodiorite, to nalite, diorite and subordinate gabbro and appinite and formed in a juvenil e magmatic are. The supracrustal rocks consist of psammites, pelites and su bordinate, interstratified mafic volcanic rocks. A Rapakivi granite suite ( 1,755-1,735 Ma) intrudes them. Gold is an important metal in the KMB and oc curs in various settings and element associations. Here, emphasis is placed on the Kangerluluk Cu-Au mineralization in the eastern part of the mobile belt. It is hosted within a remnant supracrustal succession dominated by re dundant pillowed basalts. Structurally, a syn-volcanic association with gol d can be distinguished from one that is clearly related to crosscutting qua rtz veins. In between, calc-silicate formation in the volcanic rocks occurr ed contemporaneously with a pervasive sericitization (bleaching) of leucocr atic granitoids that are intrusive into the volcanic sequence. Bulk rock an d mineral (sulfide) Pb isotope data are comparable in the Pb isotope space. The data define two groups of mineralization where one group is characteri zed by relatively higher Pb-207/Pb-204 given Pb-206/Pb-204 ratios than the other. Pb stepwise leaching (PbSL) dating experiments performed on garnet a nd epidote associated with both groups of mineralization confirm the offset in the Pb isotope data. With the geochronological information from PbSL, t he results indicate: (1) the initial gold mineralization was genetically re lated to metalliferous fluids associated with the emplacement of late intru sive stages of the Julianehab Batholith (1,800-1,770 Ma); and (2) local rem obilization of the initial mineralization (1,700-1,750) involved a Pb isoto pically evolved fluid, which tentatively can be correlated with the intrusi on of the Rapakivi granites in the area. Radiogenic Pb was not only found i n altered host rocks but also in various sulfides, suggesting that fluids m ay have percolated through and/or originated from uranium-bearing graphitic schists which are abundant in the sedimentary package of the KMB. Lead iso topic results suggest that the Rapakivi granites may have supplied heat for renewed circulation of fluids within the supra-crustal rock pile.